cleaning hub before disc pads change

The message from "Matt" contains these words:

Should do OK. Smear the mating surfaces with copper grease before reassembly so you don't have grief next time.

that will not break up the rusty scale and will leave lumps. A scraper is the right tool.

You need to scrape first with an old chisel to remove lumps of rust, then wire brush, then give a quick lick over with an oilstone to remove any high spots and make sure the surface is actually flat. You can sometimes find an

8"x2"x1" cheap Chinese chisel sharpening stone for a couple of quid at DIY stores and with paraffin or light oil as a lubricant they come in very handy for such jobs. They're bloody useless for sharpening chisels - too soft and friable and the chisel wears a groove in them first time you use it but they're excellent for licking over gasket faces, engine blocks etc. A very light smear of Copaslip is a good idea before you bolt it back on. It'll stop it rusting to the disc again.

I'd query the use of a copper based grease, like Copaslip in this application. It's primary use is as a high temperature anti-sieze assembly compound. Since the mounting faces of discs sre not subjected to high temperatures, and are not a tight fit on the hubs, I think any grease does the job equally as well, as it's purpose in this case is to help seal the disc to hub mating faces from the ingress and affects from water, and thus reduce the chances of corrosion between the two. Mike.

The temperature transmitted from the disk to the mounting flange of the hub can be pretty high. I'd rather use Copaslip than ordinary grease given there's no other downside. Anyway it helps use up that 500g tub of Copaslip all of have but only use a smidgeon of every year.

I need to do that more than most as I forgot I already had a tub many years ago and bought another before finding the first. I can't remember the last time I used any of either of them. Probably when I changed the pads on the Focus 3 years ago and that was likely less than 1cc. I bet most of the Copaslip that Molyslip sell never actually gets used but sits on someone's shelf until they die and then gets chucked. I'm going to make a mental note to slap it on everything I assemble from now on just to use the bloody stuff up.

I know what you mean. The tin I have was baught over 20 years ago. Still about a third left.

At work I use a Rocol waterproof grease for protecting steel mould inserts in injection moulds which are cooled by a constant flow of chilled water. Even after being run for up to 3 weeks 24/7, when stripped the grease has not been washed away, and the inserts show no signs of rust.

Very useful on cars. Apart from protecting discs, I use it on any chassis, engine, bolts nuts etc that are subject to water corrosion.Bolts/nuts I've treated with it are still rust free after several years. Only thing is, is that AFAIK it's only available in 2.5 litre tins, which AFAIR cost over £30, but it is very good stuff. Mike.

The message from "Mike G" contains these words:

You've never had a disc stuck to a hub? Copper grease has worked very well for me in the past in this particular application. Obviously anyone who slathers grease all over the place on brakes is asking for trouble, but a thin smear is enough.

The message from "Dave Baker" contains these words:

You could donate it to one of the car firms - life would be a lot easier if they used the stuff in the factory!

They are.

Ok sounds like the right advice.

This is the first disc and pads change I'm doing on the car as whoever did it before didn't bother with the likes of any grease. Still at least I know the job will get done properly, if the sodding rain stops that is. I wanted to do it this weekend.

Yes, but never on discs I've fitted. Only on cars I've bought, or worked on for others.

Copper grease has worked very

I know it works. Just that I don't think it's to be particularly recommended, when almost any old grease will do the job as well. If you have some why not use it, but I wouldn't recommend anyone buying some simply to fit discs if they already have some plain grease available. There's no particular advantage in using copper based greases when assembling loose fit components like discs.

Obviously anyone

Agreed. Applicable whatever type of grease is used. Mike.

The braking area of the disc certainly is, but it's mounting face and the hub flange is not. Mike.

The message from "Mike G" contains these words:

Ah, you're assuming that all dics are loose-fitting.

One day, take the discs off a Renault Trafic and see how you feel about it then. Took me nearly an hour with a lump hammer.

AFAIK they all are when new. I've never heard of discs being an interference fit on a hub by design.

But that's because of corrosion. They were not made that way. Mike.

The message from "Mike G" contains these words:

That's what the copper grease is for! Actually, the new discs were fairly tight even when I'd scraped the hubs clean.